DFT Study of Nitroxide Radicals. 1. Effects of solvent on structural and electronic characteristics of 4-amino-2,2,5,5-tetramethyl-3-imidazoline-N-oxyl

Imidazoline-based nitroxide radicals are often used as spin probes for medium acidity and polarity in different systems. In this work, using the density functional theory (DFT) approach, we have studied how physico-chemical characteristics (geometry, atomic charges and electron spin density distribution) of pH-sensitive spin label 4-amino-2,2,5,5-tetramethyl-3-imidazoline-N-oxyl (ATI) depend on protonation and aqueous surroundings. Our calculations demonstrate that ATI protonation should occur at the nitrogen atom of the imidazoline ring rather than at the amino group. Protonation of ATI leads to a decrease in a spin density on the nitrogen atom of the nitroxide fragment >N-O. For simulation of ATI hydration effects, we have constructed a water shell around a spin label molecule by means of gradual (step-by-step) surrounding of ATI with water molecules (n = 2-41). Calculated spin density on the nitrogen atom of the nitroxide fragment increased with an extension of a water shell around ATI. Both protonation and hydration of ATI caused certain changes in calculated geometric parameters (bond lengths and valence angles). Investigating how structural and energy parameters of a system ATI-(H2O)n depend on a number of surrounding water molecules, we came to the conclusion that a hydrogen-bonded cluster of n ≥ 41 water molecules could be considered as an appropriate model for simulation of ATI hydration effects.Comment: 30 pages, 11 figures, 6 table

Study on the Performance of New Imidazoline Electromigration Inhibitor in Reinforced Concrete

Steel bars inside reinforced concrete easily become corroded in high chloride environments, bidirectional electromigration rehabilitation is an important method of repairing the durability of reinforced concrete, it can migrate chloride out of concrete and transfer electromigration inhibitor to the surface of the steel bar under the action of an electric field. In this paper, autonomous synthesis electromigration inhibitor was used with bidirectional electromigration rehabilitation to repair the durability of reinforced concrete. Specifically, the effect of a new imidazoline corrosion inhibitor on chloride migration, corrosion potential, and reinforcement of concrete strength was explored. The research results showed that the dechlorination effect and electrochemical dechlorination made no significant difference on the surface of the concrete, where chlorine removal efficiency was more than 70% and the location of steel efficiency of chlorine was more than 90%. The autonomous synthesis electromigration inhibitor was found to be excellent at facilitating chloride migration and ameliorating corrosion, meanwhile, it had a negligible impact on the concrete strength

Molecular dynamics simulations and quantum chemical calculations for the adsorption of some imidazoline derivatives on iron surface

The molecular dynamic (MD) simulation and quantum chemical calculations for the adsorption of [2-(2-Henicos-10- enyl-4,5-dihydro-imidazol-1-yl)-ethyl] methylamine (HDM) and 2-(2-Henicos-10-enyl-4,5-dihydro-imidazol-1-yl)-ethanol (HDE) on iron surface was studied using Materials Studio software. Molecular dynamic simulation results indicate that the imidazoline derivative molecules uses the imidazoline ring to effectively adsorb on the surface of iron, with the alkyl hydrophobic tail forming an n shape (canopy like covering) at geometry optimization and at 353 K. The n shape canopy like covering to a large extent may prevent water from coming in close contact with the Fe surface. The quantum chemical calculation based on the natural atomic charge, the frontier molecular orbital and the Fukui indices values and plots shows the active sites of the molecules to be mainly the N=C-N region in the imidazoline ring, others include the nitrogen and oxygen heteroatoms in the pendant part and the double bonded carbon atoms in the hydrophobic tail of the imidazoline derivative molecules. The quantum chemical calculations also reveal that the amine group in HDM and the hydroxyl group in HDE which is attached to the imidazoline ring do not result in a significant increase in the HOMO nor the LUMO density which can aid adsorption. HDM has a lower energy gap of 4.434 eV and 3.824 eV, a higher EHOMO of -4.273 eV and -4.152 eV and a higher global softness of 0.45 and 0.52 compared to HDE which have an energy gap of 4.476 eV and 4.084 eV, a EHOMO of -4.349 eV and -4.607 eV and a global softness of 0.45 and 0.49 at geometry optimization and at 353 K. The adsorption ability of the molecule is given as at geometry optimization HDM > HDE and at 353 K HDM > HDE. Theoretically HDM is a better inhibitor than HDE. The adsorption ability of the molecule is in line with the binding energy at the temperature studied.Keywords: Molecular dynamic simulation; iron surface; adsorption; imidazoline derivatives; quantum chemical calculation

A Study on Multi-Functional Oilfield Production Chemicals for Scale, Corrosion and Gas Hydrates

Oilfield production chemistry is a wide field which includes many different areas and related difficulties. In this work, focus is on mitigating scale, corrosion, and gas hydrates using chemical inhibitors. Production lines often require chemical treatment for several problems simultaneously, which may cause incompatibility issues. The development of multi-functional inhibitors is based on the idea of treating all three issues simultaneously and avoiding incompatibility. As a part of this development, the ability to test the corrosion inhibition of a compound was paramount. Using the Gamry EuroCell Electrochemical Cell a CO2 corrosion testing method was reviewed and optimized to reduce deviation and increase replicability. The optimized method was used to test various compounds to investigate which functional groups that could be interesting to include in future inhibitor syntheses. The major results found from this testing were that 500 ppm of a commercial imidazoline exhibited a corrosion inhibition efficiency of 85.4±2.2 %, and that none of the synergists by themselves tested achieved higher efficiency. The compound with highest efficiency was found to be sodium lignosulfonate which exhibited an efficiency of 95.9±1.6 %. An experimental polymer based on polymaleic anhydride reacted with 3,3-dibutylaminopropylamine (DBAPA) and vinylcaprolactam (VCap), abbreviated PMA:VCap-DBAPA, was tested as a CI, both by itself and with various synergists. While the polymer by itself at 500 ppm exhibited an efficiency of 18.1±6.6 %, this was increased to above 90 % by the addition of five separate synergists at 100 ppm, of which the highest was ammonium thiocyanate at 96.0±1.5 %. Overall, synergists with thiol functional groups seemed to generally provide good synergism with PMA:VCap-DBAPA. While synergists with functional groups embedded within a ring structure generally provided poor synergism with PMA:VCap-DBAPA. Two other projects to synthesise polymers with multi-functional character were also carried out. The synthesis of poly(1-oxy-3-lactam vinylene) was successful for polyoxyvinylcaprolactam (POVCap) and polyoxyvinylpiperidone (POVPip). Copolymers of POVCap and POVPip were tested as corrosion and gas hydrate inhibitors. It was found that a copolymer of 36 % POVCap and 64 % POVPip exhibited a hydrate onset temperature of 11.6±0.1 ºC, and corrosion inhibition efficiency of 15.4±3.6 % for pure POVPip. While corrosion results were somewhat higher for copolymers at different ratios, the increased efficiency is likely due to the insoluble part of copolymers with a high molar fraction of OVCap. None of the synergists tested managed to achieve a similar synergism with POVCap as with other polymeric caprolactam containing kinetic gas hydrate inhibitors. Finally, the synthesis of hyperbranched polyamine containing imidazolidine rings based on a publication from a Chinese group was unsuccessful. Many attempts were made with different variations of the synthesis, but none were found to produce the described product

2-Imidazolines in Annulation Studies.

This thesis will describe attempts to use suitably substituted 2-imidazolines in Diels-Alder reactions. In order to synthesise these target 2-imidazolines a new and reliable method for the synthesis of 2-alkyl and 2-alkenyl-2-imidazolines has been developed. Metallation at C(2a) of l-ferf-butyloxycarbonyl-2-methyl-2-imidazoline, followed by reaction with a range of electrophiles and deprotection with TFA reliably afforded N(l)- unsubstituted 2-substituted 2-imidazolines; P- or Se-electrophiles led to 2-alkenyl-2- imidazolines via Wadsworth-Emmons reaction or selenoxide elimination. In an attempt to prepare N-butadienyl-2-imidazolines via the reaction of 2-alkyl-2-imidazolines and ɑ,ß-unsaturated aldehydes or ketones, tetrahydroimidazo[1,2-a]pyridines have been synthesised via conjugate addition of the heterocycle N(l) nitrogen atom followed by enamine-aldol condensation at C(2ɑ). 2-Imidazolines reacted with ß-ketoesters to give tetrahydroimidazo[1,2-a]pyridin- 5-ones. Whilst examining the reactions of 2-alkyl-2-imidazolines with alkyne diesters, a new annulation was uncovered that is based on N(l) conjugate addition followed by C(2ɑ) The reaction of 2-imidazolines with dialkyl acetylenedicafboxylate afforded tetrahydropyrrolo[1,2-a]imidazole-5,6-diones. None of the 2-imidazolines synthesised that contained diene functionalities underwent either intra or intermolecular Diels-Alder reactions

Applications of N-heterocyclic imines in main group chemistry

The imidazolin-2-imino group is an N-heterocyclic imino functionality that derives from the class of compounds known as guanidines. The exocyclic nitrogen atom preferably bonds to electrophiles and its electron-donating character is markedly enhanced by efficient delocalization of cationic charge density into the five-membered imidazoline ring. Thus, this imino group is an excellent choice for thermodynamic stabilization of electron-deficient species. Due to the variety of available imidazoline-based precursors to this ligand, its steric demand can be tailored to meet the requirements for kinetic stabilization of otherwise highly reactive species. Consequently, it does not come as a surprise that the imidazolin-2-iminato ligand has found widespread applications in transition-metal chemistry to furnish pincer complexes or "pogo stick" type compounds. In comparison, the field of main-group metal compounds of this ligand is still in its infancy; however, it has received growing attention in recent years. A considerable number of electron-poor main-group element species have been described today which are stabilized by N-heterocyclic iminato ligands. These include low-valent metal cations and species that are marked by formerly unknown bonding modes. In this article we provide an overview on the present chemistry of main-group element compounds of the imidazolin-2-iminato ligand, as well as selected examples for the related imidazolidin-and benzimidazolin-2-imino system

A happy medium : the synthesis of medicinally important medium-sized rings: Via ring expansion

Medium-sized rings have much promise in medicinal chemistry, but are difficult to make using direct cyclisation methods. In this minireview, we highlight the value of ring expansion strategies to address this long-standing synthetic challenge. We have drawn on recent progress (post 2013) to highlight the key reaction design features that enable successful 'normal-to-medium' ring expansion for the synthesis of these medicinally important molecular frameworks, that are currently under-represented in compound screening collections and marketed drugs in view of their challenging syntheses

Iridium-Catalyzed Enantioselective Hydrogenation of Vinylsilanes

We have screened a diverse array of iridium complexes derived from chiral N,P ligands as catalysts for the asymmetric hydrogenation of vinylsilanes, a transformation for which generally applicable catalysts were lacking. Several catalysts emerged from this study that enabled the highly enantioselective hydrogenation of a wide range of vinylsilanes with trisubstituted or disubstituted terminal C=C bonds bearing aryl, alkyl, ethoxycarbonyl, or hydroxymethyl substituents. In addition to trimethylsilyl and dimethyl(phenyl) silyl derivatives, trialkoxysilyl- and silacyclobutyl-substituted alkenes were used as substrates